Method of producing stressing cement

ABSTRACT

A stressing cement is produced by mixing 58-62% by weight of Portland cement with an expanding component taken in an amount of 38-42% by weight. The expanding component consists of calcium sulphate, calcium oxide and an aluminate-containing material such as alumina cement or calcium hydroaluminate.

A0116 1 EX United States Patent 11 1 Mikhailov et al.

1 1 Nov. 27, 1973 METHOD OF PRODUCING STRESSING CEMENT [22] Filed: May17, 1972 [21] Appl. No.: 254,314

Related US. Application Data [63] Continuation of Ser. No. 35,565, May7, 1970,

abandoned.

[52] US. Cl 106/89, 106/97, 106/102,

106/104 [51] Int. Cl C04b 7/02 [58] Field of Search 106/89, 97, 102,106/100, 103, 104

[56] References Cited UNITED STATES PATENTS 3,155,526 11/1964 Klein106/104 3,510,326 5/1970 Miki 106/104 Primary Examiner-James E. PoerAtt0rney-Waters, Roditi, Schwartz & Nissen [5 7] ABSTRACT A stressingcement is produced by mixing w by weight of W with an expandingcomponent taken in an amount of My weight. The expanding componentconsists of calcium sulphate, calcium oxide and an aluminate-containingmaterial such as alumina cement or calcium hydroaluminate.

1 Claim, No Drawings 1 METHOD OF PRODUCING STRESSING CEMENTCross-Reference to Related Application This application is acontinuation of application Ser. No. 35,565, filed May 7, 1970, and nowabandoned.

The present invention relates to methods of producing stressing cement.

Known in the art is a method of producing stressing cement by way ofmixing or milling together Portland cement and an expanding componentcomprising calcium sulphate and a substance containing calciumaluminate, for instance, alumina cement, alunite, etc. (of. U.S.S.R.Inventors Certificate No.l07,996, Class 80b,

The main distinction of stressing cement in contrast to other binderslies in that in the course of its hardening it is capable of expandingand performing mechanical work in tensioning the reinforcement ofconcrete articles, or exerting pressure on obstacles limiting itsexpansion. Thereby, a part of the liberated energy is consumed by theconcrete upsetting, thus bringing about the general self-stressing ofthe structure.

It is known that when manufacturing preliminary stressed structures thereinforcement is stressed and concrete is upset by mechanical,electrothennal and electrothermomechanical methods. The stressing cementmakes it possible to dispense with employment of various machines andmechanisms used when manufacturing preliminary stressed structures, andallows to automatically obtain preliminary stress in all the directions.Employment for the purpose of mechanical means is obtained with greatdifficulties.

Concrete and sand-and-cement mortars using the stressing cement arehighly water-, benzineand gasproof.

The afore-described properties of the binding cement, and namely thefact that it is water-, benzineand gasproof and is capable of expanding,have predetermined the main spheres of its applications: pipes,containers and other tanks used for storing water and oil products.

However, the energy of the self-stress of concrete using the bindingconcrete, both in the form of mortars and concrete, does not exceed thevalues of an order of to 40 kglcm respectively, which limits the sphereof its application.

It is an object of the present invention to provide a method ofproducing binding cement, whereby use is made of such components thatallows substantial increase in the energy of the self-stress of thiscement.

The afore-said and other objects are accomplished in that when preparingbinding cement comprising an expanding component including calciumsulphate and a substance containing calcium aluminates, in accordancewith the invention, calcium oxide is added to the expanding component.

Prior to mixing, the substance containing calcium aluminates may besubjected to hydration along with calcium oxide. It is expedient tohydrate the substance containing calcium aluminates and lime in order toob tain a high-alkaline calcium hydroaluminate at a temperature withinthe range of 20 to 150C.

During the hydration of the substance containing calcium aluminates,calcium hydroxide may be added in an amount exceeding that necessary forformation of high-alkaline calcium hydroaluminate.

i i 1 v It is known that the expansion and self-stress of a structureusing binding cement results from formation in the cement rock offirstly calcium hydrosulphoaluminate of a low-sulphate form, and thenits recrystallization into a high-sulphate form.

Calcium hydrosulphoaluminate of a low-sulphate fonn is formed when thereis not enough mixing water according to the following formula: c,Ai-i,,+cH+ c,+a aAwsmmfl mm we q In case the process is continued with waterin excess, there takes place its recrystallization into a highsulphateform according to the formula: 3 m+( )=-H )Z 4W aM h mH hq With themixing water being in excess and the temperature not exceeding 40C, itis not low sulphate but a high-sulphate form of calciumhydrosulphoaluminate that is formed at once according to the followingreaction:

4 ia' 'H )a+ q 3 )a s1 xq, where C Al-l is 4CaO-Al O 1 311 0 CH iscalcium hydroxide Ca(Ol-l),

is water C A(CS)l'-l is low-sulphate form of calciumhydrosulphoaluminate 3CaO-Al O l ZH O (C S H is gypsum sulphate (hydrategypsum) 2Ca- 41-1 0. C A(C) l-l is high-sulphate from of calciumhydrosulphoaluminate 3CaO -Al O -3CaSO 3 IH O C is gypsum sulphate(dehydrated gypsum) Ca SO The subject of the present invention lies inintensification of the processes of formation of a low-sulphates form ofcalcium hydrosulphoaluminate by creating an appropriate medium in thecouse of the binding cement setting and hardening by way of adding tothe expanding component calcium oxide which very quickly hydrates anddecreases the amount of free water in the cement rock.

To obtain a great value of the self-stress and high strength (withoutany drops), it is necessary to effect a correct control over the processof the cement expansion, which depends on the following three factors:the amount of the components used, the amount of the water and thetemperature of the medium.

When the amount of the expanding additive exceeds the optimal one theretakes place its great expansion which breaks the tight connections ofthe Portland cement rock, but due to the Portland cement hydroationwhich goes on, new connections are formed in the cement rock tocompensate the broken ones, as a result of which the strength isincreased.

It is necessary to take into account that a lowsulphate form is quicklyformed after mixing, which form is then quickly recrystallized into ahigh-sulphate one provided it is not prevented from doing so by someexterior factors. With the hardening temperatures exceeding 80C, thehigh-sulphate form of calcium hydrosulphate is produced but in smallamounts. However, introduction in the reaction products of calcium oxidefourcalcium hydroaluminate -(in excess) which absorbs a part of themixing water Mama. q-k veg-M. w...- nr-h pared from the followingmaterials taken in the following correlation (by weight per cent):

1. Alumina cement 70 2. Milled burnt lime 30 These materials had thefollowing chemical composition:

Losses durilng Chemical composition, in weight percent es el- No.Initial materials nation SiO: A1203 FezO; MgO CaO N320 K: SO;

- 1 Alumina cemenL 0. 83 8. 97 44. 43 0. 35 0. 86 42. 16 O. 0 08 23-1 2ime 0 prepared from a mixture of alumina cement and lime by way of theirmutual hydration and drying at a normal or high temperature z up to150C) which provides for quick and complete saturation of calciumaluminates with calcium oxide. Good results are obtained with excessivefree lime, in which case it is possible to dispense with separatebatching of the lime to be added to cement as it is introduced in thesystem along with the high-alkaline calcium hydroaluminate.

Thus, as a result of the present method there is produced afour-component binder providing for the selfstressing in the concrete ofup to 60-80 kg/cm, in which the presence of lime substantially altersthe process of formation and recrystallization of calciumhydro-sulphoaluminate.

When manufacturing reinforced concrete articles from concrete using thebinding cement the latter is mixed with water until an easy-to-handlemixture is obtained. In the course of its hardening the expansion of thecement rock is limited by the reinforcement and the whole energy of therecrystallization of calcium hydrosulphoaluminate is consumed by thetensioning of the reinforcement and upsetting of the concrete proper.Thereby there appears an intensive selfstressing of the reinforcedconcrete structure with all the properties of preliminary stressedreinforced concrete resulting therefrom. Due to a very great packing ofthe cement rock structure the concrete becomes water-, gasandbenzine-proof.

The above-described phenomenon is confirmed by the following examples.

EXAMPLE 1 The following initial materials were used (taken in weight percent) to prepare the binding cement: 1. Portland cement 58 2.High-alkaline calcium hydroaluminate 27.5 3. Milled building gypsum 12.54. Lime 2 The initial materials had the following chemical composition:

To produce high-alkaline calcium hydroaluminate, alumina cement and limewere carefully mixed together by hand and soluted in water added in theamount of 0.5% from the weight of the dry mixture.

After it had been carefully mixed with the water, the

25 The binding cement was prepared by way of milling its ingredients ina mill until the specific surface was 4670 cm /gr.

The qualities of the binding cement were tested as follows:

30 Samples were made of prisms of the dimenstions of 20 30 l00 mm andcubes of the dimensions of 30 30X30 mm, which were used for testingexpansion and strength, respectively.

The samples were made from sand concrete having the composition 1:1(binding cement: sand) by weight.

Sand having a fineness modulus of 2.06 was used as the filler. Theamount of the water used for preparing the concrete constituted 30 percent of the weight of the cement.

The newly prepared concrete mixture had a cone setting of 2.5 cm. Thesamples of prisms and cubes were moulded by way of slight vibration.

Reinforced prisms were manufactured to test the self-stress of theconcrete.

The lengths of the samples of prisms and reinforcement were measured andthe cubes were strengthtested twenty hours after they had beenmanufactured, i.e., at the moment of the striking, whereupon the sampleswere measured daily.

The values of the self-stress was evaluated in the reinforced prisms bymeasuring the deforrnation of the reinforcement and concrete, and innon-reinforced prisms by means of instruments having resilient stopsprecluding free elongation of the prisms in the longitudinal direction.The resilient resistance of the stops corresponded to the reinforcingcoefficient p. 1%.

The results of the tests of the concrete are given in The high-alkalinecalcium hydroaluminate was prethe following table:

- lndiccs of Age of the samples In days the concrete Age of the samplesin days Concrete indices 1 2 7 14 a 00 we the blndlng cement l 3 7 I4 28Free expansion. in percent. 8.11 8.37 8.39 8.43 8.46 8.47 Freeexpansion, Strength. in kg,/0m, 170 272 2 374 in 0.56 1.15 3.17 3.994.0l Self-stress. in kg,/cm 7.6 11.2 25.4 43.5 59.7 62.0 5 Strength.

M in kg/cm 348 282 150 350 450 Self-stress, EXAMPLE 2 in kgcm 31 41.657.3 73.2 81.3 Preparation of binding 4-component cement I Theingredients of the binding 4 component cement I The following resultshave been obtamed when testwere mixed in a ball mill by way of grinding,whereby mg the samples for PFOOfQeSSI I the initial materials wereuniformly dispersed in the the Pressure bemg 20+ 24 m-v 20 Samplesmixture so that the Specific surface was 4630 ems/gt when tested forwaterproofness, have shown no filtra- The composition of the initialmaterials (in weight leakage per cent). 2. W1th the pressure bemg atm.,the gasproofness 1. Portland cement 62 coemclem was 2. Alumina cement3.7.10" cm cmlcm sec atm. i g iii l4 3. With the pressure being 23 atm.,the benzine- 1 e u n roofness coeffic1ent was These ingradients had thefollowing chemical compop sition: 20 4.0 10" cmcm/cm sec atm Lossesduring calcin. Chemical composition, in weight percent H d in wt. y rateNo. Initial material percent SiO; A110: F010: MgO 0110 N820 KzO S0:water 1 Portland cement... 0. 80 20.73 5. 61 4.12 6.01 511.42 0.10 0.802.12 2. Alumina cement 1.05 6.66 45. 77 1.10 40. 76 0.10 0.11 0.1 3Gypsum 5. 45 0.73 0.25 3.47 33. J 48.12 9.02 4 Lime 23.14 3.30 0.460.11; 0.0 00.40 0.05 0

The qualities of the binding cement thus obtained were tested in amanner analogous to that described in Example 1.

To simultaneously test water, benzineand gasproofness, there weremanufactured conic samples, discs that were mm thick.

To test the waterproofness, water pressure was applied at the side ofthe large base of a disc, which pressure was then raised in stages for 2atm. an hour, and upon reaching 10 atm. was kept during 6 hours.Thereupon, the pressure was raised up to 20-24 atm and was kept at thislevel during 3-4 hours. A part of the samples were kept at this pressureduring l-3 days, and the pressure was controlled every 30 minutes.

To test the benzineand gasproofness, the pressure was raised by stagesfor 1 atm during 1+2 hours.

The results of the evaluation of the cement qualities are presented inthe following table:

As derived from the above Examples, the Portland cement is present inthe ingredient mixture in an amount between 58-62%, the calcium sulphatein an amount of l2.5l4%, the calcium oxide in an amount between 2-4% andthe aluminate-containing substance is an amount between 2027.5%, theamounts being in by weight.

What is claimed is:

l. A stressing cement composition consisting essentially of 58-62% byweight Portland cement and an expanding component consisting of 12.5 to14% by weight calcium sulphate, 2 to 4% by weight calcium oxide and2027.5% by weight of an aluminatecontaining material, saidaluminate-containing material being alumina cement, or high-alkalinecalcium hydroaluminate prepared by subjecting a high-alumina cement andlime mixture to joint hydration and heating to a temperature of from 20to C.

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